By Paul McBride · ·
I recently received a letter asking about engine break-in following overhaul. This is a subject that should be of interest to everyone, even though you may never actually have the opportunity to break-in an engine during your flying years.
It makes no difference whether it is a factory new, factory rebuilt, factory overhaul, or an engine overhauled in the field, the most important rule regarding engine break-in is don’t baby it! These same break-in procedures also apply if a cylinder replacement takes place during the life of the engine.
Every factory engine comes with information as to how an engine should be broken in following installation. Most field overhaul facilities also provide similar information, which may be more specific for their overhaul and should be followed to assure proper break-in occurs.
The general rule of thumb when breaking in an engine is to be certain to use the proper oil. A quick review of the latest revision of Lycoming Service Instruction 1014 should be your first stop. Most, but not all, Lycoming engines use mineral base oil for break-in, but there are exceptions to this and that information can be found in SI1014.
When I say “don’t baby it,” what that means is that using lower power settings for break-in is not recommended. Using full power for takeoff and climb is not harmful to the newly installed engine and serves the engine well for a proper break-in. However, all engine temperatures should be monitored closely to ensure overheating does not occur.
To get good ring seating, we must keep the power up during takeoff, climb and cruise in order to expand the piston rings and force them against the cylinder walls, which causes the ring to seat. I usually recommend the aircraft be cruised at 65% to 75% to accomplish good break-in. If the engine were mine, I’d use 75% power for cruise. You must also keep in mind that break-in should occur at altitudes typically under 5,000 feet where 75% power can be attained on normally aspirated engines. Density altitudes in excess of this will not allow the engine to develop sufficient cruise power for a good break-in.
From my experience, if an engine is operated properly, the break-in will usually take place within the first 25 hours or sooner. The key that will let you know break-in has occurred is when the oil consumption stabilizes. Once the oil consumption stabilizes, you may then switch to an AD (ashless dispersant) oil of your choice.
Once again, I cannot emphasize enough that you must read the engine manufacturer’s or overhauler’s recommended procedures for proper engine break-in. Failure to do this may cause improper break-in and cause high oil consumption and costly repairs to correct this situation.
Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.
About Paul McBride
Paul McBride, an expert on engines, retired after almost 40 years with Lycoming.
Send your questions to askpaul@generalaviationnews.com.
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John George saysI am about to break in a brand new IO540 in my Piper Malibu Mirage.
With the demise of the Aussie $ the cost of this unit down under is substantial so I need to get this right.
Thanks Paul for your advice, it’s like the beginning of a relationship, the proper respect has to be shown , the better it is done the longer the relationship lasts!- Michel FENOUIL says
Good evening Paul,
Following a VNIP I finished 25 hours break-in period of my O-360-A1A (with mineral oil 80), and since I put usual oil spark plugs bottom do not work (200 RPM drop on “L” selection), they are oil-fouled.
We opened the air intake pipes and we found oil in it (from where does it come ?).
Does it say that the break-in was not well done? During the break-in with mineral oil I flew 20 Hg MP and 2300 RPM instead of 75-80 % of the power. I didn’t know break-in must be done at higher power.
Mechanic advise to resume a new break-in period at 75-80 % of power.
What do think of it ?
Thank you for your help, Paul.Michel
- Jewgo Min says
Hello Paul,
Thank you for your excellent article about breaking in an aircraft engine. My question is – I have been breaking in my new car engines by “babying” the power by driving 30-40 mph for a certain number of miles, then move up to 40-50 mph for another certain number of miles and on up to 60-70 mph. So from you said in the article, this method is incorrect and I should be driving 60-70 mph right from the start or do you have to treat aircraft engines and automobile engines differently?
Jewgo Min- Michel FENOUIL says
I remember in the oldies, when my dad bought a brand new car, the break-in must be done at low speed then increasing more and more as you said.
I think it is not the same with piston aircraft engines, maybe because these engines are flanged we must break-in at a high power…
As an aviation enthusiast with a comprehensive understanding of engine break-in procedures, I find Paul McBride's article from September 5, 2012, on this subject to be quite informative. McBride, a retired expert with nearly 40 years at Lycoming, shares invaluable insights into the critical process of breaking in an aircraft engine following an overhaul.
McBride emphasizes a few key concepts that are crucial for a successful engine break-in:
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Oil Selection:
- McBride stresses the importance of using the proper oil during break-in. He recommends referring to Lycoming Service Instruction 1014 for the latest information on oil choices. While most Lycoming engines use mineral-based oil for break-in, exceptions exist, and specific details can be found in the service instruction.
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Power Settings:
- The general rule advocated by McBride is to avoid "babying" the engine during break-in. Lower power settings are discouraged, and instead, he advises using full power for takeoff and climb. Maintaining higher power settings during takeoff, climb, and cruise is essential to achieve good ring seating by expanding piston rings against cylinder walls.
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Monitoring Engine Parameters:
- McBride underscores the need to closely monitor engine temperatures to prevent overheating during the break-in process. This involves keeping a careful eye on all temperature indicators to ensure they remain within acceptable ranges.
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Cruising Power for Break-In:
- To achieve good break-in, McBride recommends cruising the aircraft at 65% to 75%, with a personal preference for 75% power during cruise. It's essential to perform the break-in at altitudes typically below 5,000 feet, allowing for the attainment of 75% power on normally aspirated engines.
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Break-In Duration:
- McBride suggests that, with proper operation, break-in usually occurs within the first 25 hours or sooner. An indicator that break-in has taken place is when oil consumption stabilizes. Once this happens, the transition to an AD (ashless dispersant) oil of choice is recommended.
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Follow Manufacturer's Recommendations:
- The overarching theme in McBride's advice is to adhere strictly to the engine manufacturer's or overhauler's recommended procedures for proper engine break-in. Neglecting this could lead to improper break-in, resulting in high oil consumption and potentially costly repairs.
Paul McBride's expertise shines through in his guidance, providing a valuable resource for pilots and aircraft owners looking to ensure the longevity and optimal performance of their engines. If you have any specific questions or need further clarification on these concepts, feel free to ask.
